This invention relates to tufting machines and more particularly to cut-pile machines of this type having knife blades for cutting loops of yarn while on the hooks shortly subsequent to the formation of the loops.
In conventional cut-pile tufting machines the loops that are formed by the cooperation of the individual needles and loop seizing blade of the hook are severed on the blade to form cut pile. To cut the loop a knife is disposed on one face of each of the hooks having a cutting edge that cooperates with the underside of the loop seizing blade. In such machines the knives are carried by an knife holder secured to an oscillating knife shaft. The knives are formed of spring steel and must be arranged at a slight angle and canter relative to the respective hook to provide tension to insure proper sissor-like cutting action between the cutting edges of the knife and hook. Quite obviously the friction between the knife and hook produces wear on the knives and hooks, and limits the speed of such machines.
To provide proper cutting without having loose or jagged ends of yarn, the cutting edge of the knives must be kept sharp. This requires periodic removal and replacement while the edges are reground. For example, in the typical prior art arrangement, such as illustrated in U.S. Pat. No. 3,386,398 of J. A. Cobble Sr. et al., two knives are set in a knife block secured to the hook shaft. Since such machines may have 1000 or more knives, replacement and resetting of the knives at the proper angles can be a tedious time consuming operation requiring significant machine downtime and labor.
Modular block constructions have been proposed in attempts to reduce downtime due to knife changes and to extend the life of the knife. For example, in German Auslegeschrift No. 23,49,800 of K-H Zieseniss, a slotted knife block is slidably mounted in a runner rail by means of a dove tail guideway and the runner rail is thereafter conventionally mounted in the knife shaft. The knives are first set in the block on a bench, and the complete block can be replaced as a unit. U.S. Pat. No. 3,212,467 of Wittler illustrates a similar concept. In these and other attempts at modules conventional tufting knives have been used with all their inherent problems.
Other deficiencies with the conventional tufting cutters include the requirement of properly timing the knife shaft to the hook shaft, and what is known as "J" cut. This is the condition where the legs of a cut loop are not the same length and thus the resulting pile height is not level. This results from the knife cutting against one face of the hook while the loop extends about the entire hook section. There have been many attempts to solve this problem using conventional knives, with varying degrees of success. Nonconventional attempts have been made using a rotary cutter acting within a slot cut in the hook. Examples of this approach are illustrated in U.S. Pat. No. 2,103,798 of Taradash, U.S. Pat. No. 3,052,198 of Whitney and Danish Pat. No. 76,466 of Bonnesen. However, these proposed constructions could not be used readily for machines operating at relatively high speeds and producing the fine gauge tufted product required by today's market.